Conventional color television picture tubes are manufactured with discrete dots of phosphors of three different colors. Three electron beams are utilized to excite the phosphor dots of the three colors, respectively. Precise positioning of the three electron beams is necessary for each beam to excite the phosphor dots of its associated color. Stray magnetic fields and manufacturing variations of color picture tubes generally result in the beams failing to register with the associated phosphor dots, thus requiring beam correction which is effected by bending the electron beams with a magnetic field produced by purifying magnets. Beam correction devices are well known in the art, as described in U.S. Pat. No. Re. 27,209 of Robert R. Malone entitled BLUE LATERAL AND PURITY MAGNET ASSEMBLY, and U.S. Pat. No. 4,065,737 of the present inventor entitled STATIC CONVERGENCE DEVICES FOR COLOR TELEVISION PICTURE TUBES. Such beam convergence devices are in the form of an assembly which has a channel extending therethrough for accommodating the neck of a color television picture tube, and the assembly is secured to the picture tube by means of a clamp.
In recent years, great efforts have been made to reduce the size and cost of television sets. Such efforts have resulted in television color picture tubes with substantially shorter necks which have permitted a reduction in depth of the cabinet for the television sets. The use of such tubes, and the other reductions in size, have placed a demand for space within the cabinet of the television set, and made it desirable to materially decrease the size of convergence assemblies.
Convergence assemblies also introduce magnetic fields into the cabinet which may affect the functioning of certain components in addition to the color picture tube. Stray fields from the convergence assembly can be confined by reducing the size of the convergence assembly and therefore a reduction in the size of such convergence assemblies is further desirable.
It is also desirable to reduce the cost of convergence assemblies for an in-line color picture tube, but provide a convergence assembly which will facilitate precise adjustment of the three beams with the phosphor areas associated with the beams, respectively.